Electron discharge device



LU H W HHM .5u/550e? INVENTOR.

F. L. SALISBURY ELECTRON DISCHARGE DEVICE Filed March 25. 1954 QN l@ S QJune 23, 1959 United States Patent Varian Associates, `Sau Carlos,Calif., a corporation of California Application Marchas, 11954,'sena1No. v418,714 z claims. (ci. sis- 5.39)

invention 'relatesto electron discharge devices and, more particularly,to anelectrondischarge device of the velocity modulation type arrangedto operate at microwave 'frequencies las an amplifier.

As @the operating frequency of electron discharge devices or tubes -hasincreased, a corresponding increase has been noted with respect to thecritical nature of `the alignment `of Athe elements -thereof, thegeometric shape and tolerancesof such'elements, and the -losses of`energy resulting from Lanyldeviationin these tube design factors. Whilevthe design problems presented have been severe with `tubes suchas -reexklystrons and two-cavity klystron amplifiers, they have ibeenfurtheraccentuated, for obvious reasons, with multi-cavity klystrons,particularly lwhen frequencies of *the -order of 20-30 -`lerne. areapproached. In such cases,sincefa wavelength is in the neighborhood ofv1 centimeter, even Asuch minor structural :aberrations as produced by'bracing can laffect -the losses :and the tunability -ofthe amplifier.

Accordingly, a feature of the present invention involves the provisionof a multi-cavity microwave amplifier of relatively y'simplelconstruction and lha-ving optimum gain characteristics.

A further feature 'is the provision of a microwave amplifier of .-the`multi-cavity type having a structural farrangement whichfacilitatesassembly `andeiilcient operation thereof.

Yet another feature `of lthe yinvention is the provision of a 'microwaveamplifier structurally arranged 'to insure proper alignment of Atheparts and the maintenance of design tolerances.

These 'and other features will become more .appa-rent from thenfollowing description :of 'a preferred embodiment of the present:invention as shown in the accompanying drawings wherein:

Fig. 1 4is an elevational .view of `a multi-cavity micro- 'waveamplifier, vparts Ibeing fcut .away to illustrate features ofconstruction,

Fig. .2 `is 'a section taken along line 2-2 of Fig. l, and

=Fig. 3 is 'anfenlarged view partially inzsection illustrating interiorconstruction of the resonator cavities of the amplier.

The microwave ampliierig'enerally Iincludes a beamproducing section.C10lfollowed 'hty 'a central section 11 wherein the interaction betweenthe beam and the applied radio frequency wave takes place 'to providethe amplication and facollector section '12 where the electrons `of thespent Abeam are collected.

lin accordance with the invention, the amplification section 11 .of thetube preferably has a body formed from asubstantially semi-cylindrical:block 13 of/copper, as best illustrated in Fig. 2. A cylindrical bore14 which extends longitudinally through the semi-cylindrical block 13 isintersected by a number of spaced transverse bores 15 extending from theflattened side 21 of the block 13 and is adapted to receive a pluralityof drift-tube memice a bers 17. Each member 17 comprises a coppercylinder which 'is .provided with small cylindrical lextensions 18 atits ends Vand has a central bore extending therethrough and throughVsuch extensions to provide a drift space 19 for "the electron beam.When the members 17 are inserted inthe bore 14 in properly spacedrelation, as determined by the spacing of the transverse bores 15,resonator cavities 16 of the desired frequency are formed betweenadjacent members. Prior to insertion of the copper drift-tube members 17into Vthe bore 14, the latter is provided 'by a'liash-plating techniquewith a thin layer of silver. 'The exterior Vdimension of the drift tubemembers 17 is slightly greater than the diameter of the plated bore 14through the described semi-cylindrical block 13 so that upon insertion.a pressed-fit is obtained. After the insertion of the drift tubemembers 17, a single heating operation will cause the copper and silverVto alloy and the members to be fused within the bore. It should belnoted that the same fusing technique and resulting assembly can beemployed with drift tube members 17 which are not of solid copperconstruction; for example, copperclad molybdenum drift tube members canbe utilized in the fabrication. This technique obviously avoids thementioned diliiculty of conventional brazing methods and a cleanjuncture is formed between the drift tube members 17 and the bore 14which provide, in effect, the walls ofthe resonator cavities 16.

An inner drift tube member 17 which is machined to provide thetheoretically' desiredgeometry to as close tolerances as possible is.first inserted and, 'in turn, each of the adjacent drift tube members17 is inserted to an extent slightly less than that required to providethe spacing productive of the desired resonant frequency of the cavities1'6. Subsequently, radio frequency energy is .supplied to each cavity 16between adjacent drift tube members through the respective one of thetransverse bores V15 extending Vfrom the Viiattened-side 21 of thesemi-,cylindrical .block 13. While radio frequency energy of .thedesired frequency is inserted through the transverse bore 15 a Vslightaxial movement is imparted to the drift tube member 17 until theresonance condition is achieved, vthis then being the final dispositionof the member. The above described technique has been found not Vonlydesirable but Vactually indispensable to vproduce the desired -cavitydimensions when operating at frequencies between 2O and 30 kmc. becauseat such frequencies :normal machining operations have insufficientaccuracy to effect the desired structural tolerances.

AAs is shown clearly in Fig. 3, the first and last cavities 16 of 4theillustrated five-cavity amplifier are completed by members 17 which ineffect constitute onehal-f ofthe complete drift tube members 17previously described, in the intermediate portions of the bore 14.

To .provide coupling of radio frequency energy into and out oftheamplifier, the described semi-cylindrical block 13 is -cut away in itslower portion for the reception of conventional waveguide sections 22which cornmunicate with the first and last resonator cavities 16 throughbored iris openings 23. A mica window 2.4 is suitably Asecured at theend of each of the waveguide sections 22 to maintain the vacuum withinthe cavities 16 and the remainder of the tube.

The ,previously mentioned bores 15 are enlarged adjacent theflattenedside 21 of the semi-cylindrical block 13 `as vindicated at 20to receive in vacuum-tight relation a `tuning diaphragm 25 secured atthe end of a tuning screw-'26 which is adjustably suspended from thelateral arrnj27a of a bracket 27 secured vto the flattened side 21 ofthe block 13 by suitable screws 28. The diaphragms 25 are maintained inadjusted position by pairs of lock nuts 29, 30 on the tuning screws 26which nuts engage 3 respectively the upper and lower surfaces of thelateral bracket arm 27a.

The beam-producing section includes a substantially cylindrical hollowbody 31 having a cathode button 32 and associated heater element 33 andfocusing ring 34 mounted centrally therein and axially aligned with atapered bore 35 formed in the base of an attached pole piece 36 ofmagnetic material and adapted to register with the aligned drift spaces19 in the drift-tube members 17, 17' within the amplification section 11of the tube. To assure that such alignment is achieved, the cathodebutton 32 is provided with a small central aperture 32a which enablesthe cathode 32 and the drift tube members 17, 17 of the tube to bealigned optically; that is, a light may be positioned at the end of thebeam-producing section 10 and the same laterally shifted until suchlight passes through the small central aperture 32a in the cathodebutton 32, the registering bore 35 in the pole piece 36 and the drifttube members 17, 17 so as to be visible to a viewer whose eye isadjacent the drift space 19 at the output end of the amplificationsection 11. While so aligned the beam-producing section 10 or moreparticularly the attached pole piece 36 is aunularly brazed or otherwisesecured to the amplication section 11 of the tube so that the alignmentwill be maintained.

The collector section 12 of the electron discharge device is preferablymounted on the second cup-shaped pole piece 38 having a tapered bore 39extending centrally through its base and adapted to register with thealigned drift spaces 19 when said cup-shaped element is brazed inposition at the output end of the amplification section 11 of the tubeso as to accommodate the electron beam. Such alignment is again attainedby the optical technique described above. The collector section 12includes an elongated member 40 having a deep cylindrical recess 41machined therein and arranged so that its open end is adjacent and axialwith the tapered bore 39 in the pole piece 38. The two elements aresecured in such relation through a glass-to-metal seal 42 formed betweentubular stubs 43, 44 extending in opposite directions from an annularcap 45 on the cup-shaped pole piece 38 and a thick sleeve 46 telescopedonto the outer end of the elongated collector member 40. Thisconstruction and insulated mounting of the collector enables currentreadings to be taken when desired.

Tubulations 47 in the side of the two pole pieces 36, 38 enableevacuation of the tube after completion of the assembly, and are thenpinched-off as shown in Fig. 1. To facilitate evacuation, eccentricaxially-extending passages 48 are formed in the drift tube members sincethe actual diameter of the ldrift spaces 19 will be somewhat less than.02l at the mentioned operating frequencies. Because these passages 48are relatively well below cutoff at the operating frequency, no radiofrequency energy can be transmitted therethrough.

The tube is electrically connected quite conventionally, a battery 50being arranged, as shown in Fig. 1 to provide heater current, and asecond battery 51 to provide positive D.C. voltage `for the central andcollector sections 11, 12 of the tube. Conventional coils indicated atS2, 53 are disposed adjacent the pole pieces 36, 38 to provide forproper focusing of the beam during its traverse through the tube. Inoperation, the beam of electrons emitted from the cathode button 32 isaccelerated through the bore 35 and into the small cylindrical boresthrough the drift tube members 17. The radio frequency signal to beamplified is fed into the first or buncher cavity resonator through theinput waveguide 22. The radio frequency electric field produced acrossthe resonator gap in this first cavity resonator velocity modulates theelectrons, that is, the electrons are slowed down or speeded updepending on the phase of the radio 4 frequency field across the gap atthe time of transit of the electron. In the held-free drift spacedefined by the rst drift tube member 17 and extensions 18, the velocitymodulation forms the beam into groups or bunches of electrons which, attheir point of sharpest bunching, pass through the resonator gap in thesecond cavity resonator. All of the cavity resonators are soproportioned as to size and gap spacing as to be sharply resonant at thedesired operating frequency of this cascade amplifier. The cavityresonators are initially tuned during assembly by the proper positioningand brazing of the drift tube members 17 to establish lcorrect resonatorgap spacing, the cavities thereafter being fine-tuned by means of theycliaphragrns 25. All of the cavity resonators between the rst or inputresonator and the last or output resonator serve to improve the bunchingof the electron beam initiated in the first cavity resonator so thatoptimum bunching is produced before the beam passes through theresonator gap in last or output resonator. The arnplifled radiofrequency energy is passed out from this cascade amplifier through theoutput waveguide 22. An actual tube which has been constructed andoperated with 1500 volts on the sections 11, 12 has produced a gain ofas high as 74 decibels, as a result of the minimization of lossesthrough the described arrangement in accordance with the invention. Whatlosses do occur, of course, appear as heat in the amplification andcollector sections 11, 12 of theV tube and are easily dissipated becauseof the large volume of the semi-cylindrical block i3 and the thicksleeve 46 on the collector member 40, no cooling fins being requiredaSince many modifications and variations in the described arrangement canobviously be made without departing from the scope of the invention, itis intended that all matter in the foregoing description or shown in thedrawing shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

l. An electron discharge device comprising an electron beam-producingsection, an electron collecting section, a. microwave amplificationsection disposed between said first and second named sections comprisinga metallic body with a longitudinal bore extending therethrough, a thinlayer of high electrically-conducting soldering material coated on thesurface of the bore, and a plurality of drift tube members disposedwithin said bore in spaced relation whereby a plurality of resonatorcavities are formed therein the drift tube members being secured withinthe bore fused to said layer of electrically-conducting solderingmaterial, said drift tube members having axial bores therein throughwhich said beam passes and having eccentrically disposed passagestherein parallel to said axial bores and of dimensions such that thetransmission of energy of the resonant frequency of said dischargedevice through said passages is precluded.

2. An electron discharge device according to claim 1 wherein said drifttube members are of copper and the coat on the surfacel of a said boreis a thin layer of silver.

References Cited in the lc of this patent UNITED STATES PATENTS JimenezMay 3l, 1955

